Effects of rimonabant on the development of single dose-induced behavioral sensitization to ethanol, morphine and cocaine in mice

RATIONALE

The endocannabinoid system has been implicated in the neurobiological mechanism underlying drug addiction, especially the primary rewarding dopamine-dependent processes. Therefore, endocannabinoid receptor antagonists, such as the CB1 cannabinoid antagonist rimonabant, have been proposed as candidates for preventive addiction therapies.

OBJECTIVES

Investigate the possible involvement of CB1 receptors in the development of behavioral sensitization to ethanol, morphine and cocaine in mice.

METHODS

We compared the effects of different doses of rimonabant (0.3, 1, 3 and 10mg/kg) on spontaneous locomotor activity in the open-field, hyperlocomotion induced by acute administration of ethanol (1.8g/kg), morphine (20mg/kg) or cocaine (10mg/kg) and on subsequent drug-induced locomotor sensitization using a two-injection protocol in mice. We also investigated a possible depressive-like effect of an acute rimonabant challenge at the highest dose and its potential anxiogenic property.

RESULTS

At the highest dose, rimonabant abolished ethanol- and cocaine-induced hyperlocomotion and behavioral sensitization without modifying spontaneous and central locomotor activity or inducing depressive-like behavior on the forced swim test in mice. The other doses of rimonabant also selectively blocked acute ethanol-induced central hyperlocomotion. Although rimonabant at 0.3 and 1mg/kg potentiated the central hyperlocomotion induced by acute morphine injection, it was effective in attenuating morphine-induced behavioral sensitization at all doses.

CONCLUSIONS

Because the neural basis of behavioral sensitization has been proposed to correspond to some components of addiction, our findings indicate that the endocannabinoid system might be involved in ethanol, cocaine and morphine abuse.

Discrimination of excess toxicity from narcotic effect: influence of species sensitivity and bioconcentration on the classification of modes of action

The toxicity data of 2624 chemicals to fish, Daphniamagna, Tetrahymenapyriformis and Vibriofischeri were used to investigate the effects of species sensitivity and bioconcentration on excess toxicity. The results showed that 47 chemical classes were identified as having the same modes of action (MOAs) to all four species, but more than half of the classes were identified as having different MOAs. Difference in chemical MOAs is one of the reasons resulting in the difference in toxic effect to these four species. Other important reasons are the difference in sensitivity and bioconcentration of species. Among the four species, V. fischeri has the most compounds identified as reactive MOA. This may be due to some compounds can be easily absorbed into the bacteria, react with the DNA or proteins, disrupt the normal function of the cell and exhibit significantly greater toxicity to the bacteria. On the other hand, the skin and lipid content of aqueous organisms can strongly inhibit the bio-uptake for some reactive compounds, resulting in a less toxic effect than expected. D. magna is the most sensitive species and T. pyriformis is the least sensitive species of the four species. For a comparison of interspecies toxicity, we need to use the same reference threshold of excess toxicity. However, some reactive compounds may be identified as baseline or less inert compounds for low sensitive species from the threshold developed from high sensitive species. The difference in the discrimination of excess toxicity to different species is not only because of the difference in MOAs for some compounds, but also due to the difference in sensitivity and bioconcentration.

Determining pharmacological selectivity of the kappa opioid receptor antagonist LY2456302 using pupillometry as a translational biomarker in rat and human

BACKGROUND

Selective kappa opioid receptor antagonism is a promising experimental strategy for the treatment of depression. The kappa opioid receptor antagonist, LY2456302, exhibits ~30-fold higher affinity for kappa opioid receptors over mu opioid receptors, which is the next closest identified pharmacology.

METHODS

Here, we determined kappa opioid receptor pharmacological selectivity of LY2456302 by assessing mu opioid receptor antagonism using translational pupillometry in rats and humans.

RESULTS

In rats, morphine-induced mydriasis was completely blocked by the nonselective opioid receptor antagonist naloxone (3mg/kg, which produced 90% mu opioid receptor occupancy), while 100 and 300 mg/kg LY2456302 (which produced 56% and 87% mu opioid receptor occupancy, respectively) only partially blocked morphine-induced mydriasis. In humans, fentanyl-induced miosis was completely blocked by 50mg naltrexone, and LY2456302 dose-dependently blocked miosis at 25 and 60 mg (minimal-to-no blockade at 4-10mg).

CONCLUSIONS

We demonstrate, for the first time, the use of translational pupillometry in the context of receptor occupancy to identify a clinical dose of LY2456302 achieving maximal kappa opioid receptor occupancy without evidence of significant mu receptor antagonism.

A new real-time method for detecting the effect of fentanyl using the preoperative pressure pain threshold and Narcotrend index: a randomized study in female surgery patients

Individual variability in the effects of opioid analgesics such as fentanyl remains a major challenge for tailored pharmacological treatment including postoperative analgesia. This study aimed to establish a new real-time method for detecting the effects of fentanyl and their individual differences in the preoperative period, using the pressure pain threshold (PPT) and Narcotrend index (NTI) test.Eighty women undergoing elective surgery under general anesthesia were enrolled in this randomized, double-blinded, placebo-controlled study to receive either intravenous fentanyl (Group F) or saline (Group S). Before (T1) and 5 (T2) and 10 min (T3) after intravenous injection, the PPT, NTI, respiratory rate, heart rate, blood pressure, and pulse oxygen saturation were measured. The initial time at which the Narcotrend index showed a decline was also recorded.In total, 40 patients in Group S and 38 patients in Group F were included in the final analysis. At 5 min and 10 min after intravenous fentanyl administration, the analgesic effect was determined by measuring the PPT, which was significantly increased (P < 0.001), and the sedative effect was detected using the NTI, which was significantly decreased (P < 0.001). The distribution of percentage changes of the PPT and NTI showed individual differences. At T2 and T3, the absolute changes in NTI and PPT were positively correlated (r = 0.444 at T2, P = 0.005; r = 0.332 at T3, P = 0.042).Through the PPT and NTI, it was feasible to easily detect the effects of fentanyl and their individual differences in real time before induction of anesthesia in the operation room. This method could potentially be applied to preoperatively determine patients' sensitivity to fentanyl.

Explicit and implicit heroin-related cognitions and heroin use among patients receiving methadone maintenance treatment

BACKGROUND

Craving is an important issue in substance use disorder. To achieve a better understanding of the cognitive processing systems of craving, the cognitive processes of craving have been considered as two distinct processes. One system, based on rule-based inferences and named explicit cognition, is more conscious and effortful. The other system, based on prior learned association and named implicit cognition, is unconscious and effortless. How explicit and implicit cognitions are associated with heroin use in patients with methadone maintenance treatment (MMT) is not clear. This study aimed to explore the relationship between explicit and implicit cognition and heroin use in patients undergoing MMT.

METHOD

This study recruited one-hundred forty intravenous heroin users. The participants were invited to provide social-demographic data, the severity of substance dependence and explicit cognition with regard to heroin. Then, participants completed a computerized test to assess implicit cognition with regards to heroin.

RESULTS

This study found that explicit and implicit heroin-related cognitions were associated with the frequency of heroin use. There was an interaction effect between implicit and explicit cognition on the frequency of heroin use. This study also found that higher explicit heroin-related cognition was a risk factor for continuing heroin use.

CONCLUSION

Both explicit and implicit cognitions were associated with the frequency of heroin use in patients undergoing MMT, but only explicit cognition was associated with whether patients could stop using heroin during MMT. Therefore, the status of heroin use in patients undergoing MMT may be related to different cognitive processes.

Behavioral flexibility and response selection are impaired after limited exposure to oxycodone

Behavioral flexibility allows individuals to adapt to situations in which rewards and goals change. Potentially addictive drugs may impair flexible decision-making by altering brain mechanisms that compute reward expectancies, thereby facilitating maladaptive drug use. To investigate this hypothesis, we tested the effects of oxycodone exposure on rats in two complementary learning and memory tasks that engage distinct learning strategies and neural circuits. Rats were trained first in either a spatial or a body-turn discrimination on a radial maze. After initial training, rats were given oxycodone or vehicle injections in their home cages for 5 d. Reversal learning was tested 36 h after the final drug exposure. We hypothesized that if oxycodone impaired behavioral flexibility, then drug-exposed rats should learn reversals more slowly than controls. Oxycodone exposure impaired spatial reversal learning when reward contingencies changed rapidly, but not when they changed slowly. During rapid reversals, oxycodone-exposed rats required more trials to reach criterion, made more perseverative errors, and were more likely to make errors after correct responses than controls. Oxycodone impaired body-turn reversal learning in similar patterns. Limited exposure to oxycodone reduced behavioral flexibility when rats were tested in a drug-free state, suggesting that impaired decision-making is an enduring consequence of oxycodone exposure.

Involvement of insular muscarinic cholinergic receptors in morphine-induced conditioned place preference in rats

RATIONALE

Drug addiction represents a pathological usurpation of neural processes involved in learning and memory. Retrieval of drug-related memories can result in drug craving and relapse. Recently, the insula was identified as part of the neuronal circuit responsible for the processing of drug memory; however, its precise role remains unclear.

OBJECTIVE

To investigate the involvement of insular muscarinic acetylcholine receptors (mAChRs) in the processing of drug memory.

METHOD

The morphine-induced conditioned place preference (CPP) was used to assess drug memory. All rats were first trained with morphine to establish the CPP. Sub-groups of these rats were used for contextual cue-induced CPP reinstatement. Other sub-groups of rats underwent extinction of the CPP, and 5 m/kg morphine was used for priming-induced CPP reinstatement. Microinjection of mAChR antagonists or agonists into the insula was performed prior to the CPP tests in order to evaluate their effect on CPP expression.

RESULTS

Insular microinjections of the nonselective mAChR antagonist, scopolamine, and the M₁ antagonist, pirenzepine, significantly inhibited CPP expression in both contextual cue- and priming-induced CPP reinstatement; the M₁ agonist, MCN-A-343, and the M₄ antagonist, tropicamide, enhanced CPP expression. The M₄ agonist, LY2033298, inhibited CPP expression. The M₂ antagonist, methoctramine, and M₃ antagonist, 4-DAMP, had no effect on CPP expression.

CONCLUSION

Our results demonstrate that insular mAChRs play a role in the processing of drug memory. M₁ and M₄ mAChRs work paradoxically; M₁ activation and M₄ inhibition attenuate the expression of drug memory, while M₁ inhibition and M₄ activation augment the expression of drug memory.

[Therapy in heroin addiction]

Heroin addiction is one of the most devastating and expensive of public health problems. The most effective treatment is opioid replacement therapy. Replacement of heroin, a short-acting euphoriant with methadone or other opioids that have significantly longer duration of action provides a number of therapeutic benefits. Opioid detoxification has a role in both preventing acute withdrawal and maintaining long-term abstinence. Opioid-based detoxification is based on the principle of cross-tolerance, in which one opioid is replaced with another one that is slowly tapered. For the treatment of heroin addicts a wide range of psychosocial and pharmacotherapeutic treatments are available; of these, methadone maintenance therapy has the most evidence of benefit. Methadone maintenance reduces and/or eliminates the use of heroin, reduces the death rate and criminality associated with heroin use, and allows patients to improve their health and social productivity. In addition, enrollment in methadone maintenance has the potential to reduce the transmission of infectious diseases associated with heroin injection, such as hepatitis and HIV. The principal effects of methadone maintenance are to relieve narcotic craving, suppress the abstinence syndrome, and block the euphoric effects associated with heroin. There is growing interest in expanding treatment into primary care, allowing opioid addiction to be managed like other chronic illnesses. Buprenorphine which is a long-acting partial agonist was also approved as pharmacotherapy for opioid dependence. Opioid antagonists can reduce heroin self-administration and opioid craving in detoxified addicts. Naltrexone, which is a long-acting competitive antagonist at the opioid receptors, blocks the subjective and objective responses produced by intravenous opioids. Naltrexone is employed to accelerate opioid detoxification by displacing heroin and as a maintenance agent for detoxified formerly heroin-dependent patients who want to remain opioid-free.

Blockade of orexin-1 receptors in the ventral tegmental area could attenuate the lateral hypothalamic stimulation-induced potentiation of rewarding properties of morphine

The orexins (hypocretins) are lateral hypothalamic (LH) neuropeptides that have been implicated in a variety of behaviors ranging from feeding to sleep and arousal. Evidence from animal models suggests a role for orexins in reward processing and drug addiction. In the present study, we investigated the direct effect of an orexin antagonist in the ventral tegmental area (VTA) on acquisition and expression of morphine conditioned place preference (CPP) induced by concurrent stimulation of the LH. Eighty-one adult male Wistar rats weighing 220-280 g were unilaterally implanted by two separate cannulae into the LH and VTA. The CPP paradigm was done; conditioning score and locomotor activity were recorded by Ethovision software. The animals received SB334867 as a selective orexin-1 receptor antagonist (0.1, 1 and 10 nmol/0.3 μl DMSO) in the VTA, just 5 min prior to intra-LH administration of ineffective dose of carbachol as a cholinergic agonist (62.5 nmol/0.5 μl saline) that stimulates orexin neurons in the LH and ineffective dose of morphine (1 mg/kg, subcutaneously) concurrently during conditioning phase (acquisition experiments) or post-conditioning phase (expression experiments). Data showed that the blockade of orexin-1 receptors in the VTA could inhibit the acquisition (development) but not expression of LH stimulation-induced morphine CPP in the rats. Our findings suggest that the orexinergic projections from the LH to the VTA are involved in the development of the LH stimulation-induced potentiation of morphine rewarding properties and orexin-1 receptors in the VTA have a substantial role in this phenomenon.

Regulatory effects of chronic low-dose morphine on nitric oxide level along with baroreflex sensitivity in two-kidney one-clip hypertensive rats

INTRODUCTION

Opiates are traditionally used for treatment of some acute heart disorders. There are only few reports on the effects of long-term treatment of cardiovascular diseases with morphine. This study aimed to investigate the effects of chronic low-dose morphine use on the cardiovascular system in two-kidney one-clip (2K1C) hypertensive rats.

MATERIALS AND METHODS

Male Wistar rats were divided into two groups as the sham and 2K1C groups and each group was further subdivided into saline and morphine treatment subgroups. Blood pressure, heart rate, plasma rennin activity, serum nitric oxide concentration, and baroreflex sensitivity were measured.

RESULTS

Morphine significantly attenuated systolic blood pressure, diastolic blood pressure, and mean arterial pressure in the 2K1C animals. In addition, morphine decreased plasma rennin activity in the 2K1C group. Serum concentrations of nitric oxide were also decreased, and morphine prevented the reduction of nitric oxide. The baroreflex sensitivity was also improved following morphine administration in the 2K1C group.

CONCLUSIONS

According to the results presented in this study, chronic administration of low-dose morphine reduces regulated hypertension in the 2K1C rats, probably via a nitric oxide-dependent pathway.

Dysregulation of dopaminergic regulatory mechanisms in the mesolimbic pathway induced by morphine and morphine withdrawal

Dopamine (DA) is thought to represent a teaching signal and has been implicated in the induction of addictive behaviours. Previously, it has been proposed that the transcription factors Nurr1 and Pitx3, which are critical for transcription of a set of genes involved in DA metabolism in the mesolimbic pathway, are associated with addiction pathology. The aim of our study was to investigate abnormalities in the mesolimbic pathway associated with morphine dependence and withdrawal. Using quantitative real-time PCR, immunofluorescence, HPLC and Western blotting, here we studied the effects of single morphine administration, morphine dependence and morphine withdrawal on Nurr1 and Pitx3 expression as well as on the DA marker tyrosine hydroxylase (TH) and the turnover of DA in the ventral tegmental area (VTA) and/or nucleus accumbens. We showed that the three experimental conditions caused induction of Nurr1 and Pitx3 in the VTA, which correlated with changes in TH expression during chronic morphine administration. Present data also confirmed the colocalization of Nurr1 and Pitx3 with TH-positive neurons in the posterior VTA. Furthermore, during morphine dependence, Nurr1 was detected in the nucleus compartment of VTA TH-positive neurons, whereas Pitx3 was strongly detected in the nucleus of TH-positive neurons after single morphine administration and during morphine withdrawal. The number of TH neurons, number of Nurr1 or Pitx3-positive cells, and the number of TH neurons expressing Nurr1 or Pitx3 were not modified in the subpopulations of DA neurons. Present data provide novel insight into the potential correlation between Nurr1 and Pitx3 and DA neurons plasticity during opiate addiction in the mesolimbic pathway.

Pharmacological activation of kappa opioid receptors: aversive effects in adolescent and adult male rats

RATIONALE

The dynorphin (DYN)/kappa opioid receptor (KOR) system is involved in the dysphoric properties of drugs of abuse. Given that adolescents show reduced sensitivity to aversive effects of many drugs, alterations in the DYN/KOR system may contribute to the prevalence of drug use during adolescence.

OBJECTIVES

The present study was designed to assess dysphoric properties of a selective kappa agonist, U62,066, in adolescent and adult rats using both conditioned taste aversion (CTA) and conditioned place aversion (CPA) paradigms.

METHODS

For CTA, water-restricted rats were administered U62,066 following 30 min access to a saccharin solution, with subsequent saccharin consumption used to index aversion. For CPA, animals were allowed access to both compartments of a two-compartment chamber for a 15-min pre- and post-conditioning test. For conditioning, subjects were administered U62,066 prior to confinement to one side of the chamber and saline prior to confinement to the other side for a total of four pairings.

RESULTS

Overall, adolescents displayed reduced sensitivity to the kappa agonist relative to adults. Adults demonstrated taste aversions to the 0.2 and 0.3 mg/kg doses of U62,066, whereas adolescents did not display aversions to any tested doses. Adults demonstrated a place aversion to the 0.1 and 0.2 mg/kg dose of U62,066 when paired with the preferred side of the conditioning chamber. Adolescents did not display aversions to any of the doses tested.

CONCLUSIONS

Reduced sensitivity to DYN/KOR system activation during adolescence may be a contributing factor to the age-typical insensitivity to aversive properties of drugs commonly abused by adolescents.

Effects of amphetamine and methylphenidate on delay discounting in rats: interactions with order of delay presentation

RATIONALE

Drug effects on delay discounting are thought to reflect changes in sensitivity to reinforcer delay, although other behavioral mechanisms might be involved. One strategy for revealing the influence of different behavioral mechanisms is to alter features of the procedures in which they are studied.

OBJECTIVE

This experiment examined whether the order of delay presentation under within-session delay discounting procedures impacts drug effects on discounting.

METHODS

Rats responded under a discrete-trial choice procedure in which responses on one lever delivered one food pellet immediately and responses on the other lever delivered three food pellets either immediately or after a delay. The delay to the larger reinforcer (0, 4, 8, 16, and 32 s) was varied within session and the order of delay presentation (ascending or descending) varied between groups.

RESULTS

Amphetamine (0.1-1.78 mg/kg) and methylphenidate (1.0-17.8 mg/kg) shifted delay functions upward in the ascending group (increasing choice of the larger reinforcer) and downward in the descending group (decreasing choice of the larger reinforcer). Morphine (1.0-10.0 mg/kg) and delta-9-tetrahydrocannabinol (0.32-5.6 mg/kg) tended to shift the delay functions downward, regardless of order of delay presentation, thereby reducing choice of the larger reinforcer, even when both reinforcers were delivered immediately.

CONCLUSION

The effects of amphetamine and methylphenidate under delay discounting procedures differed depending on the order of delay presentation, indicating that drug-induced changes in discounting were due, in part, to mechanisms other than altered sensitivity to reinforcer delay. Instead, amphetamine and methylphenidate altered responding in a manner consistent with increased behavioral perseveration.

An examination of the validity of the standardized field sobriety test in detecting drug impairment using data from the Drug Evaluation and Classification program

OBJECTIVE

The purpose of this study is to assess the validity of the 3 components of the Standardized Field Sobriety Test (SFST), including the Horizontal Gaze Nystagmus (HGN), One Leg Stand (OLS), and Walk and Turn (WAT) tests, in identifying impairment among suspected drug-impaired drivers using data recorded during drug evaluation and classification (DEC) evaluations.

METHODS

Data from 2142 completed DEC evaluations of central nervous system (CNS) stimulants, CNS depressants, narcotic analgesics, cannabis, or no drugs were analyzed using multinomial logistic regression.

RESULTS

All drug categories were significantly associated with impaired performance. On the HGN, users of CNS depressants were significantly more likely to experience lack of smooth pursuit and distinct nystagmus at maximum deviation compared to non-drug users. On the OLS, users of all drug classes were significantly more likely to sway while balancing and use their arms to maintain balance but significantly less likely to hop compared to drug-free cases. Users of CNS depressants, CNS stimulants, and narcotic analgesics were significantly more likely to put their raised foot down during the test. On the WAT, users of CNS depressants, CNS stimulants, and narcotic analgesics were significantly less likely to keep their balance while listening to test instructions compared to those who had not used drugs. Users of CNS depressants were less likely to touch heel-to-toe while walking, whereas individuals who had used narcotic analgesics were less likely to take the correct number of steps.

CONCLUSIONS

These findings provide support for the use of the SFST as a screening tool for law enforcement to identify impairment in persons who have used CNS stimulants, CNS depressants, cannabis, or narcotic analgesics.

Differential effect of beta-adrenergic receptor antagonism in basolateral amygdala on reconsolidation of aversive and appetitive memories associated with morphine in rats

Positive and negative emotional experiences induced by addictive drugs play an important role in the development of dysfunctional drug-related memory, which becomes resistant to extinction and contributes to high rate of relapse. Those memories may undergo a process called reconsolidation that in some cases can be disrupted by pharmacological treatment. The basolateral amygdala (BLA) has been shown to mediate the reconsolidation of drug-related appetitive memory, but its role in withdrawal-related aversive memory remains elusive. The present study used conditioned place preference (CPP) and conditioned place aversion (CPA) paradigms to investigate the role of BLA and its noradrenergic receptors in reconsolidation of morphine-associated emotional memory in rats. We found that inhibition of protein synthesis in BLA disrupted the reconsolidation of morphine CPP (m-CPP) and CPA related to morphine withdrawal (m-CPA). A high dose of the β-noradrenergic receptor antagonist propranolol (3 µg) in BLA-impaired reconsolidation of m-CPA but not m-CPP, whereas a low dose (0.3 µg) was ineffective. In contrast, neither low nor high doses of the α-noradrenergic receptor antagonist phentolamine (1 or 10 µg) blocked the reconsolidation of m-CPP and m-CPA. In addition, infusion of propranolol (3 µg) into nucleus accumbens after retrieval of either m-CPP or m-CPA did not affect its reconsolidation. The findings indicate that appetitive and aversive addictive memories share common neural substrates in BLA, but the specific neurotransmitter mechanism on reconsolidation of morphine-associated negative and positive memories can be dissociable.

[Behavioural studies during the gestational-lactation period in morphine treated rats]

Opioids impair the maternal behaviour of experimental animals. The effect of morphine on maternal behaviour in rat dams treated chronically with morphine during the whole pregnancy and lactation has not been yet analysed systematically.

OBJECTIVE

The aim of our work was to investigate the behavioural effects of moderate dose morphine administered constantly in the whole perinatal period in rats.

METHODS

Nulliparous female rats were treated with 10 mg/kg morphine s.c. once daily, from the day of mating. Maternal behaviour was observed, the effects of acute morphine treatment on the maternal behaviour and whether this effect could be antagonised by naloxone were also investigated. Physical and other behavioural (anxiety-like signals in elevated plus maze, changes in locomotor activity) withdrawal signs precipitated by naloxone were registered. After weaning sensitivity to the rewarding effect of morphine was measured by conditioned place preference and to the aversive effect of naloxone by conditioned place aversion tests. Antinociceptive test on tail-flick apparatus was performed to investigate the changes in morphine antinociceptive effects due to chronic morphine treatment.

RESULTS

Maternal behaviour was significantly impaired in morphine-treated dams. This effect of morphine lasted c.a. 2-3 hours a day, it showed dose-dependency and was enhanced in MO-treated group (sensitisation). Only weak physical and no other behavioural (anxiety-like behaviour or hypolocomotion) withdrawal signs were precipitated by naloxone. The positive reinforcing effect of morphine and aversive effect of naloxone were markedly increased on conditioned place paradigm. Significant antinociceptive tolerance was not seen.

CONCLUSION

Although human drug abuse can be hardly modelling under experimental circumstances, our constant, relatively moderate dose morphine treatment administered once daily during the whole pregnancy and lactation resulted in several subtle behavioural changes in dams. In perinatally opioid-exposed offspring short- and long-term behavioural disturbances can be detected which is well-known from literature. Besides direct pharmacological effects of morphine impaired maternal responsiveness and pup care could play a role in these disturbances.

Regional expression of extracellular signal-regulated kinase 1 and 2 mRNA in a morphine-induced conditioned place preference model

Chronic morphine administration has been shown to change the expression of extracellular signal-regulated kinase (ERK), which is a molecule known to play an important role in homeostatic adaptations caused by addictive drugs. In the present study, we investigated the expression of ERK messenger ribonucleic acid (mRNA) of the prefrontal cortex (PFC), nucleus accumbens (NAc), hippocampus, and caudate putamen (CPu) in morphine-induced conditioned place preference (CPP) by real-time reverse transcriptase polymerase chain reaction (real-time PCR). CPP was established by alternate morphine (10 mg/kg) injections, extinguished after a 10-day extinction training, and reinstated by a priming injection of morphine (10 mg/kg). During three phases of morphine-induced CPP, the expression levels of ERK1 and ERK2 mRNA were altered in various brain regions. In the PFC, the expression levels of ERK1 and ERK2 mRNA were increased after chronic morphine injection (p=0.003, p=0.000), and did not return to the basal level after extinction training (p=0.025, p=0.000), but decreased after a priming injection (p=0.000, p=0.000). In the CPu, ERK1 mRNA had an abrupt increase following a priming injection (p=0.000). Different from other brain regions, the expression levels of ERK1 and ERK2 mRNA were decreased in three phases of morphine-induced CPP in the hippocampus (ERK1: p=0.000, p=0.040, p=0.000; ERK2: p=0.000, p=0.000, p=0.000, respectively). These results suggest region-specific changes of ERK1 and ERK2 mRNA expression during morphine-induced CPP.

Role of central and peripheral opiate receptors in the effects of fentanyl on analgesia, ventilation and arterial blood-gas chemistry in conscious rats

This study determined the effects of the peripherally restricted μ-opiate receptor (μ-OR) antagonist, naloxone methiodide (NLXmi) on fentanyl (25μg/kg, i.v.)-induced changes in (1) analgesia, (2) arterial blood gas chemistry (ABG) and alveolar-arterial gradient (A-a gradient), and (3) ventilatory parameters, in conscious rats. The fentanyl-induced increase in analgesia was minimally affected by a 1.5mg/kg of NLXmi but was attenuated by a 5.0mg/kg dose. Fentanyl decreased arterial blood pH, pO2 and sO2 and increased pCO2 and A-a gradient. These responses were markedly diminished in NLXmi (1.5mg/kg)-pretreated rats. Fentanyl caused ventilatory depression (e.g., decreases in tidal volume and peak inspiratory flow). Pretreatment with NLXmi (1.5mg/kg, i.v.) antagonized the fentanyl decrease in tidal volume but minimally affected the other responses. These findings suggest that (1) the analgesia and ventilatory depression caused by fentanyl involve peripheral μ-ORs and (2) NLXmi prevents the fentanyl effects on ABG by blocking the negative actions of the opioid on tidal volume and A-a gradient.

Ligand-gated purinergic receptors regulate HIV-1 Tat and morphine related neurotoxicity in primary mouse striatal neuron-glia co-cultures

Emerging evidence suggests that opioid drugs, such as morphine and heroin, can exacerbate neuroAIDS. Microglia are the principal neuroimmune effectors thought to be responsible for neuron damage in HIV-infected individuals, and evidence suggests that opioid drugs acting via μ opioid receptors in microglia aggravate the neuropathophysiological effects of HIV. Key aspects of microglial function are regulated by the P2X family of ATP activated ligand-gated ion channels. In addition, opioid-dependent microglial activation has been reported to be mediated through P2X4 signaling, which prompted us to investigate whether the cation-permeable P2X receptors contribute to the neurotoxic effects of HIV and morphine. To address this question, neuron survival, as well as other endpoints including changes in dendritic length, extracellular ATP levels, and intracellular calcium levels, were assayed in primary neuron-glia co-cultures from mouse striatum. Treatment with TNP-ATP, a non-selective P2X antagonist, prevented the neurotoxic effects of exposure to morphine and/or HIV Tat, or ATP alone, suggesting P2X receptors mediate the neurotoxic effects of these insults in striatal neurons. Although P2X7, and perhaps P2X1, receptor activation decreases neuron survival, neither P2X1, P2X3, nor P2X7 selective receptor antagonists prevented Tat and/or morphine-induced neurotoxicity. These and other experiments indicate the P2X receptor family contributes to Tat- and morphine- related neuronal injury, and provide circumstantial evidence implicating P2X4 receptors in particular. Our findings reveal that members of the P2X receptor family, especially P2X4, may be novel therapeutic targets for restricting the synaptodendritic injury and neurodegeneration that accompanies neuroAIDS and opiate abuse.

Diverse regulation of IP3 and ryanodine receptors by pentazocine through σ1-receptor in cardiomyocytes

Although pentazocine binds to σ1-receptor (σ1R) with high affinity, the physiological relevance of its binding remains unclear. We first confirmed that σ1R stimulation with pentazocine rescues contractile dysfunction following pressure overload (PO)-induced cardiac hypertrophy ovariectomized (OVX) female rats. In in vivo studies, vehicle, pentazocine (0.5-1.0 mg/kg ip), and NE-100 (1.0 mg/kg po), a σ1R antagonist, were administered for 4 wk (once daily) starting from the onset of aortic banding after OVX. We also examined antihypertrophic effects of pentazocine (0.5-1 μM) in cultured cardiomyocytes exposed to angiotensin II. Pentazocine administration significantly inhibited PO-induced cardiac hypertrophy and rescued hypertrophy-induced impairment of cardiac dysfunctions such as left ventricular end-diastolic pressure, left ventricular developed pressure, and left ventricular contraction and relaxation (±dp/dt) rates. Coadministration of NE-100 with pentazocine eliminated pentazocine-induced amelioration of heart dysfunction. Interestingly, pentazocine administration inhibited PO-induced σ1R reduction and inositol-1,4,5-trisphosphate (IP3) receptor type 2 (IP3R2) upregulation in heart. Therefore, the reduced mitochondrial ATP production following PO was restored by pentazocine administration. Furthermore, we found that σ1R binds to the ryanodine receptor (RyR) in addition to IP3 receptor (IP3R) in cardiomyocytes. The σ1R/RyR complexes were decreased following OVX-PO and restored by pentazocine administration. We noticed that pentazocine inhibits the ryanodine-induced Ca(2+) release from sarcoplasmic reticulum (SR) in cultured cardiomyocytes. Taken together, the stimulation of σ1R by pentazocine rescues cardiac dysfunction by restoring IP3R-mediated mitochondrial ATP production and by suppressing RyR-mediated Ca(2+) leak from SR in cardiomyocytes.

[The clinical and X-ray classification of osteonecrosis of the low jaw]

OBJECTIVE

To elaborate a clinical and X-ray classification of osteonecrosis of the low jaw in people with desomorphine or pervitin addiction.

MATERIAL AND METHODS

Ninety-two patients with drug addiction who had undergone orthopantomography, direct frontal X-ray of the skull, and multislice computed tomography, followed by multiplanar and three-dimensional imaging reconstruction were examined. One hundred thirty four X-ray films and 74 computed tomographic images were analyzed.

RESULTS

The authors proposed a clinical and X-ray classification of osteonecrosis of the low jaw in people with desomorphine or pervitin addiction and elaborated recommendations for surgical interventions on the basis of the developed classification.

CONCLUSION

The developed clinical and X-ray classification and recommendations for surgical interventions may be used to treat osteonecroses of various etiology.

Opioid abusers' ability to differentiate an opioid from placebo in laboratory challenge testing

BACKGROUND

Abuse liability assessments influence drug development, federal regulation, and clinical care. One suggested procedure to reduce variability of assessments is a qualification phase, which assesses whether study applicants adequately distinguish active drug from placebo; applicants failing to make this distinction are disqualified. The present analyses assessed differences between qualification phase qualifiers and non-qualifiers.

METHODS

Data were collected from 23 completers of the qualification phase of an abuse liability study. Opioid abusing participants received 30 mg oxycodone and placebo orally on separate days, and were characterized as qualifiers (vs. non-qualifiers) if their peak visual analog scale liking rating for oxycodone was at least 20 points higher than placebo's peak rating. Groups were compared on demographic characteristics, drug history, and physiologic, subject and observer ratings.

RESULTS

61% of participants were qualifiers and 39% were non-qualifiers. Groups had similar demographic characteristics, drug use histories, and pupillary constriction responses. However, unlike qualifiers, non-qualifiers had an exaggerated placebo response for the liking score (p=0.03) and an attenuated oxycodone response for the liking score (p<0.0001). Non-qualifiers' failure to differentiate oxycodone versus placebo was evident for subject and observer ratings.

CONCLUSION

Different subjective responses to identical stimuli support the use of a qualification phase in abuse liability assessments. Further research should explore objective measures that may better account for these differences, determine optimal qualification criteria, and explore the developmental course of drug use. This study also documents certain opioid abusers fail to differentiate 30 mg of oxycodone from placebo, a phenomenon deserving further study.

Morphine treatment selectively regulates expression of rat pituitary POMC and the prohormone convertases PC1/3 and PC2

The prohormone convertases, PC1/3 and PC2 are thought to be responsible for the activation of many prohormones through processing including the endogenous opioid peptides. We propose that maintenance of hormonal homeostasis can be achieved, in part, via alterations in levels of these enzymes that control the ratio of active hormone to prohormone. In order to test the hypothesis that exogenous opioids regulate the endogenous opioid system and the enzymes responsible for their biosynthesis, we studied the effect of short-term morphine or naltrexone treatment on pituitary PC1/3 and PC2 as well as on the level of pro-opiomelanocortin (POMC), the precursor gene for the biosynthesis of the endogenous opioid peptide, β-endorphin. Using ribonuclease protection assays, we observed that morphine down-regulated and naltrexone up-regulated rat pituitary PC1/3 and PC2 mRNA. Immunofluorescence and Western blot analysis confirmed that the protein levels changed in parallel with the changes in mRNA levels and were accompanied by changes in the levels of phosphorylated cyclic-AMP response element binding protein. We propose that the alterations of the prohormone processing system may be a compensatory mechanism in response to an exogenous opioid ligand whereby the organism tries to restore its homeostatic hormonal milieu following exposure to the opioid, possibly by regulating the levels of multiple endogenous opioid peptides and other neuropeptides in concert.